Gov. David A. Paterson signed into law some of the nation’s strongest protections against wage theft on Monday, after months of lobbying by immigrants’ advocates and labor unions that said New York lagged behind other states on the issue.

The law, which takes effect in April, will quadruple the penalties for employers who steal workers’ pay, and will protect whistle-blowers from retaliation.

Employers who pay below the minimum wage, fail to pay overtime or unfairly garnishee wages are especially rampant in restaurant, retail and construction businesses where illegal immigrants make up much of the work force, according to a report this year by the National Employment Law Project. In New York City, the report said, lost wages add up to more than $18.4 million a week.

“These issues go unreported and unaddressed because if you speak up you’re likely to be terminated,” Mr. Paterson said in a news conference. “There’s no administrative remedy; there’s no voice. That ends today.”

Under the old law, employers found to have stolen workers’ wages had to repay the money with a penalty of 25 percent.

“The fines were so minimal that a lot of these rogue employers saw them as the cost of doing business,” said State Senator Diane J. Savino, a Democrat from Staten Island who was the bill’s lead sponsor. Under the new law, the employers’ penalty will be up to 100 percent.

The law removes technicalities that required whistle-blowers to cite the section of the law that the employer broke. It also allows up to $10,000 in added penalties for employers who fire or threaten workers for speaking out.

“At long last, this puts real teeth in New York’s labor law,” said Andrew Friedman, co-director of Make the Road New York, an immigrants advocacy group that pushed for the bill, joined by the Retail, Wholesale and Department Store Union.

Opponents of the bill, which the Legislature passed largely along partisan lines, say it will simply create paperwork for employers who do not steal wages. “Now all employers in the state have this new regime to prevent them from doing something the vast majority of them never think of doing,” said Kenneth Adams, president and chief executive of the Business Council of New York State.

A national trend toward strengthening worker-protection laws has already taken hold in states like Massachusetts, New Mexico and Illinois, said Rebecca Givan, an assistant professor at the Cornell University School of Industrial and Labor Relations. She called the New York law “a really big success for workers.”

Maria, a Mexican immigrant who asked that her last name be withheld because she was in the country illegally, said she had worked 70 hours a week at a lamp factory in Manhattan that denied her overtime for more than a year. Make the Road New York helped her recoup almost $10,000 this year. “The new law is very great because this won’t happen to someone else,” Maria said.